Fix warning about eek receiver being set to nil, capture strong reference
Squashed commit of the following:

commit 35b4e1abd727ab9a5fb1489d73d4985a18efd138
Author: Mattt Thompson <m@mattt.me>
Date:   Thu Dec 5 14:22:49 2013 -0800

    Minor formatting

commit 36007b0f147dba1db2d46d26389a76aa339ecf0d
Merge: c25c49a c7ab4ad
Author: Mattt Thompson <m@mattt.me>
Date:   Thu Dec 5 14:11:40 2013 -0800

    Merge branch 'AFURLConnectionOperation-isFinished-without-being-started-fix' of github.com:sampage/AFNetworking into sampage-AFURLConnectionOperation-isFinished-without-being-started-fix

commit c7ab4adc0794d3fc95fa44448c8c1ac59d25df9b
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 19:23:48 2013 +1100

    Adds unit tests to cover cancelling an operation before it has begun. Rolls back previous test changes to logic of cancelling after the operation has started.

commit 412d8265eb9915f935ff3c3891dc81497a5db725
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 19:23:01 2013 +1100

    Previous change would mean operations in-flight would not be cancelled. On cancel, check whether the operation is currently executing and if so, cancel the operation immediately.

commit a522bd7daf0034b6a8527b54a00f87e5155815d1
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 18:08:01 2013 +1100

    Updates AFHTTPRequestOperationTests that cover cancelling to adhere to new logic of operations receiving -start after being cancelled

commit fbe385f8e4e11a9fb3e24c663b0c283a9caeb7bf
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 18:07:02 2013 +1100

    Removing explicit call to set state to AFOperationFinishedState. Happens as a product of cancelConnection and setting here will mean the connection is not cancelled.

commit b71eaa8c8dbb272b36345d3983d6ff3d27ebcce6
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 17:10:23 2013 +1100

    Matching conditionals formatting

commit 270066c102dc922b1adee8aff4b5ba2035676d9f
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 16:35:43 2013 +1100

    Checks whether AFURLConnectionOperation isCancelled during start, if so, cancel the connection and mark state as AFOperationFinishedState. Removes connection cancelling call from NSOperation’s cancel method.
    Fixes an issue with iOS 6.1 where cancelling an operation before it had been started would crash after logging “AFHTTPRequestOperation xxx went isFinished=YES without being started by the queue it is in”

commit 72295f6282c9eb3aa934949a6ae2d0a762712de0
Author: Sam Page <page.sam.c@gmail.com>
Date:   Wed Dec 4 16:31:07 2013 +1100

    Removes cancelled flag from AFURLConnectionOperation, instead relying on the default NSOperation isCancelled.
    Removes KVO notifications for isCancelled flag to adhere to docs: “..Support for cancellation is voluntary but encouraged and your own code should not have to send KVO notifications for this key path..”

Signed-off-by: Mattt Thompson <m@mattt.me>